Here is a (first) article dedicated to the description of all the different tipologies of batteries based on lithium. A more technical post will follow.
The present article will try to give a better understanding of how batteries (or, better, accumulators) based on lithium work. Let’s start by saying that the article will be divided into 2 different parts: the first one will define this technology using a plain and easy language, while the more technology-addicted readers will be able top appreciate the second section of the article and get a more in-depth representation of the subject.
General notes about accumulators
A battery is a device that converts chemical energy into electrical energy and vice versa.
All the accumulators have the following specifications, that the user should know to choose the correct element for his/her needs. Or just to grant an appropriate maintenance.
- Nominal voltage: The reported or reference voltage of the battery, also sometimes thought of as the “normal” voltage of the battery.
- Nominal capacity: The coulometric capacity, the total Amp-hours available when the battery is discharged at a certain discharge current (specified as a C-rate) from 100 percent state-of-charge to the cut-offvoltage. Capacity is calculated by multiplying the discharge current (in Amps) by the discharge time (in hours) and decreases with increasing C-rate.
- Technology: Not all batteries are created equal, even batteries of the same chemistry. The main trade-off in battery development is between power and energy: batteries can be either high-power or high-energy, but not both.The technology defines the type of chemical elements used to design and produce the battery. We have different technologies at the moment: Ni-Mh, Ni-Cd, Li-Ion, Li-Po, Li-Fe. Every technology has its pros and cons.
- Cells, modules and packs: A cell is the smallest, packaged form a battery can take and is generally on the order of one to six volts. A module consists of several cells generally connected in either series or parallel. A battery pack is then assembled by connecting modules together, again either in series or parallel.
- Maximum Continuous Discharge Current: The maximum current at which the battery can be discharged continuously. This limit is usually defined by the battery manufacturer in order to prevent excessive discharge rates that would damage the battery or reduce its capacity. A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this battery would be 500 Amps.
Note that if a full recharged battery goes under the threshold of 80% related to the original values, the battery is considered unusable, and you can throw it away.
Advantages/Disadvantages/Maintenance
Lithium batteries have been produxed since 1992. Lithium-ion (Li-Ion) batteries are the most widespread, but Li-Po and Li-Fe are used as well.
- Cut-off voltage between 3 e 4,1V.
- Nominal voltage 3,6V.
- Optimal specific power: from 150 to 200 Wh/Kg.
- No memory effect and no need of programmed maintenance cycles.
- Dangerous. They need an internal circuit to work, that protects them from overcharges, voltage peaks or too quick discharges limited between 1C and 2C. The circuit features a temperature sensor to avoid fires or explosions).
- They are damaged due to time, regardless of use. Have a lifespan of a few years, and lose efficiency after the first one.
This kind of battery does not require any particular maintenance, but to keep them for a long time you need to follow some simple rules.
Avoid recharging at 100% and don’t keep them charged for a long time. It is necvessary to often recharge them, so that they work in a charge range of 20-80%.
| Storage temperature | 40% of charge | 100% of charge |
|---|---|---|
| 0 °C (32 °F) | 2% loss after 1 year | 6% loss after 1 year |
| 25 °C (77 °F) | 4% loss after 1 year | 20% loss after 1 year |
| 40 °C (104 °F) | 15% loss after 1 year | 35% loss after 1 year |
| 60 °C 140 °F) | 25% loss after 1 year | 40% loss after 3 months |
- Nominal voltage 3,7V
- Cut-off voltage between 3V – 4.2V
The Li-Po batteries belong to the same family of the Li-Ion, but feature a different internal element which grant them to be more plastic. This in turn allows the creation of batteries having virtually any shape. There are few differences between Li-Po and Li-Ion batteries, but the Li-Po category seems to have a better acceptance.
In fact unlike the Li-Ion, the Li-Po batteries do not suffer from wear due to aging, but have limited recharge cycles.
In practice, the lifespan of a Li-Po battery will be similar ot the lifespan of a Li-Ion technology, if it will be used a lot. Instead, if it will be recharged less often, it will have a better lifespan through the years. Not considering here the better efficience during the years. Finally, the Li-Po battery features a better specific power, 20% higher than the Li-Ion ones.
The only disadvantage is the dangerousness. Li-Po batteries are quite delicate, and require specific power supplies to avoid explosions.
Hint: always buy strong power supplies to recharge your batteries.
These batteries are relatively new, aqnd have peculiar characteristics.
Their worst specific power and a slightly lower voltage relative to the other two families represent their only negative side.
Here is a table with all the specifications.
| Battery type | Lead | NiCd | NiMH | LiCo (LiIon or LiPo) | LiMn (LiIon) | LiFePO4 |
|---|---|---|---|---|---|---|
| Year of commercialization | 1956 | 1990 | 1990 | 1992 | 1997 | 2004 |
| Security | Good | Good | Good | Bad | Good | Excellent |
| Green product | No | No | Yes | No | Yes | Yes |
| Charge at high temperatures | Good | Good | Poor | Good | Bad | Good |
| Memory effect | No | Yes | Small | No | No | No |
| Nominal voltage | 2V | 1.25V | 1.25V | 3.7V | 3.7V | 3.2V |
| Specific Energy (Wh/Kg) | 30 | 57 | 80 | 167 | 110 | 115 |
| Specific Power (W/Kg) | 300 | 400 | 600 | 900 | 500 | >2500 |
| Lifecycle (discharge 1C) | 400 | 500 | 500 | >500 | >500 | >2000 |
| Lifespan | 1-2 years | 3 years | 3 years | 2 years | 2 years | 5-6 years |
| Charge efficiency | 60% | 75% | 70% | 90% | 90% | 95% |
| Charge time (hours) | 8 | 1.5 | 4 | 2-4 | 2-4 | 0.25-1 |
| Autodischarge (monthly) | 20% | 15% | 30% | 10% | 10% | 0.8% |
At the moment, the most effective batteries for a mobile system are the accumulators in Li-Po technology.
Anyway, the Li-Fe technology looks quite promising. In fact they have amazing specs and are the family that look most helpful towards the environment, among the lithium-based batteries.
Here is the end of the first part of the article. A second part, more technical, will be published shortly.
Luigi_Morelli
Definire ciò che si è non risulta mai semplice o intuitivo, in specie quando nella vita si cerca costantemente di migliorarsi, di crescere tanto professionalmente quanto emotivamente. Lavoro per contribuire al mutamento dei settori cardine della computer science e per offrire sintesi ragionate e consulenza ad aziende e pubblicazioni ICT, ma anche perche’ ciò che riesco a portare a termine mi dà soddisfazione, piacere. Così come mi piace suonare (sax, tastiere, chitarra), cantare, scrivere (ho pubblicato 350 articoli scientfici e 3 libri sinora, ma non ho concluso ciò che ho da dire), leggere, Adoro la matematica, la logica, la filosofia, la scienza e la tecnologia, ed inseguo quel concetto di homo novus rinascimentale, cercando di completare quelle sezioni della mia vita che ancora appaiono poco ricche.